Project Summary: Structural studies of MCM complex Minichromosome maintenance protein (MCM) complex functions as a helicase that unwinds DNA to provide template for DNA replication and plays a critical role in regulating cell growth. MCM helicases are considered to be a licensing factor for cellular DNA replication. MCM proteins from eukaryotes and archaea form hexamers ring complex, with MWt approximating 0.5-1.0 Mega Dolton. Despite extensive efforts, gap of knowledge exists in our understanding of how MCM unwinds DNA, how MCM interacts with DNA during unwinding, and how ATP is utilized to drive the conformational changes of MCM needed for unwinding. MCM are conserved in archaea and eukaryotes. Eukaryotic MCM contains six homologs that form hetero-hexamer and possibly higher order complexes. However, the MCM complex in some archaea contains only one MCM protein that can assemble into homo-hexamers or dodecamers. Thus, archaeal MCM homo-oligomers provide a simpler system for understanding the structure/function of MCM complex. The goal of this proposal is to use archaeal MCM complexes as a model system to understand the structure/functions of MCM complex, with particular emphasis on the mechanisms regarding oligomerization, ATP-triggered conformational changes, and DNA binding and remodeling functions of MCM proteins. A combination of structural biology, biophysics, and functional biochemistry will be employed for the study. The resulting data will provide valuable information for understanding the DNA unwinding mechanism at the replication fork. It will also provide structural/functional insights for the homologous eukaryotic MCM complex, which bears high relevance to cell growth regulation and cancer biology.